Whereas static routes are typically configured manually, routing protocols generate dynamic routes. Each method has advantages and disadvantages in specific network scenarios, as discussed in the following sections.

Static Routing

The term static routing denotes the use of manually configured or injected static routes for traffic forwarding purposes. Using a static route might be appropriate in the following circumstances:

■ When it is undesirable to have dynamic routing updates forwarded across slow bandwidth links, such as a dialup link

■ When the administrator needs total control over the routes used by the router

■ When a backup to a dynamically learned route is necessary

■ When it is necessary to reach a network that is accessible by only one path (a stub network)

Configuring and maintaining static routes is time-consuming. Properly implementing static routes requires complete knowledge of the entire network.

Dynamic Routing

Dynamic routing allows the network to adjust to changes in the topology automatically, without administrator involvement. A static route cannot dynamically respond to changes in the network. If a link fails, the static route is no longer valid if it is configured to use that failed link, so a new static route must be configured. If a new router or new link is added, that information must also be configured on every router in the network. In a very large or unstable network, these changes can lead to considerable work for network administrators. It can also take a long time for every router in the network to receive the correct information. In situations such as these, it might be better to have the routers receive information about networks and links from each other using a dynamic routing protocol. Dynamic routing protocols must do the following:

■ Find sources from which routing information can be received (usually neighboring routers)

■ Select the best paths toward all reachable destinations, based on received information

■ Maintain this routing information

■ Have a means of verifying routing information (periodic updates or refreshes).